The patent document EP 0 487 982 A2 discloses an electronic article surveillance system according to the fourth paragraph that is operated according to a method of operating an electronic article surveillance system according to the seventh paragraph by utilizing a read/write station according to the third paragraph and a number of data carriers according to the second paragraph, each data carrier comprises a circuit according to the first paragraph. In the known system the read/write station releases a message signal that represents a electronic article surveillance status test-request command and a data carrier comprising status data, which status data indicate whether an electronic article surveillance status is active or not active, receives the message signal and responds in case that the status data represent that the electronic article surveillance status is active for said data carrier. In order to define a first electronic article surveillance zone and a second electronic article surveillance zone that is different from the first zone said patent document discloses to provide a jamming apparatus for generating a jamming signal that allows to jam up the message signal of the read/write station within the second electronic article surveillance zone. By providing these measures data carrier being located in the second electronic article surveillance zone will not respond to the message signal released by the read/write station.
The prior art system shows the problem that such overlapping or superposition of signals does allow to define relatively large electronic article surveillance zones in which data carrier that are located either in the first zone or in the second zone do show a different behavior in the meaning of responding or not responding to a message signal. On the other hand such a system does not allow to associate a particular data carrier with the first zone or with the second zone, because the different electronic article surveillance zones are solely defined by the signals produced either by the read/write station or by the jamming apparatus and the superposition of these field, which defines one zone being different from another zone that does not show a superposition of said signals.